Thermal evolution of Tethyan surface waters during the Middle-Late Jurassic: Evidence from δ 18 O values of marine fish teeth

Thermal evolution of Tethyan surface waters during the Middle-Late

Jurassic: Evidence from D18O values of marine fish teeth

Christophe Lecuyer,1,2 Stephanie Picard,1 Jean-Pierre Garcia,3 Simon M. F. Sheppard,4

Patricia Grandjean,1 and Gilles Dromart1

Received 9 November 2002; revised 27 March 2003; accepted 16 May 2003; published 25 September 2003.

[1] Oxygen isotope compositions of phosphate from vertebrate tooth enamel were measured to determine theevolution of tropical sea surface (<�200 m depth) temperatures in the western Tethys during the Middle-LateJurassic. On the basis of a high-resolution stratigraphic framework with a 1 Myr time resolution, vertebrate teethwere sampled on Aalenian to Portlandian isochrons over the Anglo-Paris Basin. Asteracanthus sharks andPycnodontidae teleosteans, identified as sea surface dwellers, have enamel with d18O values that range from 18.5to 22.3%. Thermal variations of tropical surface waters, with amplitudes of a few degrees per few million years,suggest that Middle to Late Jurassic climates were quite variable. Assuming a seawater d18O value of 0% forsurface tropical waters in the absence of polar ice caps, temperatures increased from 25 to 29�C from the mid-Bajocian to mid-Bathonian. During the middle to late Bathonian, a strong geographic zonation in isotopiccompositions is observed between the eastern and western parts of the basin. High d18O values of fish toothenamel (up to 22.3%) could reflect the arrival of a cold water current from the Arctic during the opening of theNorth Sea rift. An apparent large drop of temperatures from 28 to 21�C is identified at the Callovian-Oxfordianboundary over no more than �2–3 Myr. This cooling is compatible with previous paleobotanical andgeochemical studies and can be precisely correlated with the migration of boreal ammonites into the Tethyandomain. Because isotopic sea surface temperatures are probably too low to be compatible with tropical climaticconditions, the d18O value of seawater could have been >0% owing to limited growth of continental ice duringthe early middle Oxfordian. The resulting sea level fall is estimated to be at least 50 m and is compatible with aglobal regression stage. The middle Oxfordian thermal minimum is followed by a new warming stage of 3–4�Cfrom the middle to the late Oxfordian. INDEX TERMS: 1040 Geochemistry: Isotopic composition/chemistry; 1045

Geochemistry: Low-temperature geochemistry; 1620 Global Change: Climate dynamics (3309); KEYWORDS: oxygen isotope, phosphate,

shark, Jurassic, seawater, climate

Citation: Lecuyer, C., S. Picard, J.-P. Garcia, S. M. F. Sheppard, P. Grandjean, and G. Dromart, Thermal evolution of Tethyan surface

waters during the Middle-Late Jurassic: Evidence from d18O values of marine fish teeth, Paleoceanography, 18(3), 1076,

doi:10.1029/2002PA000863, 2003.

1. Introduction

[2] The Jurassic has long been considered to have been awarm and equable period of Earth history, based on floral andfaunal distribution patterns [e.g., Frakes and Francis, 1990;Frakes et al., 1992; Hallam, 1998]. However, recent paleo-botanical [e.g., Philippe and Thevenard, 1996; Hubbard andBoulter, 1997; Morgans et al., 1999; Riding and Hubbard,1999; Van Aarssen et al., 2000] and oxygen isotope studieson belemnites and brachiopods [e.g.,Ditchfield, 1997; Veizeret al., 1997; Podlaha et al., 1998; Riboulleau et al., 1998]

have provided evidence for fluctuations of both paleotemper-atures and humidity during the Jurassic. Continuous paleo-climatic curves, however, cannot be established from thelimited, and fragmentary database of samples from variablewater depths.[3] Fossil biogenic apatite, especially enamel, shows

more resistance than carbonate shells to oxygen isotopeexchange during diagenesis [Kolodny et al., 1983; Kolodnyand Raab, 1988; Lecuyer et al., 1993]. Biogenic apatites,that crystallize in apparent equilibrium with seawater, haved18O values that are fixed by the temperature and theisotopic composition of water [Longinelli and Nuti, 1973;Kolodny et al., 1983]. Empirical fractionation equationshave been determined with present-day invertebrate andvertebrate ectotherms, leading to a single temperature-de-pendent curve [Longinelli and Nuti, 1973; Kolodny et al.,1983; Lecuyer et al., 1996a]. This intrinsic property of thephosphate oxygen-water system can be applied to extinctspecies to derive past temperatures, assuming a d18O valuefor the environmental water. The oxygen isotope composi-tion of well-preserved biogenic apatites has already beensuccessfully used as a marine paleothermometer [Kolodny

PALEOCEANOGRAPHY, VOL. 18, NO. 3, 1076, doi:10.1029/2002PA000863, 2003

1Laboratoire Paleoenvironnements et Paleobiosphere UMR CNRS5125, Centre Nationale de Recherche Scientifique, Campus de la Doua,Universite Claude Bernard Lyon 1, Villeurbanne, France.

2Also at Institut Universitaire de France, Paris, France.3Centre des Sciences de la Terre, Centre Nationale de Recherche

Scientifique, Universite de Bourgogne, Dijon, France.4Laboratoire de Sciences de la Terre, Centre Nationale de Recherche

Scientifique, Ecole Normale Superieure de Lyon, Lyon, France.

Copyright 2003 by the American Geophysical Union.0883-8305/03/2002PA000863$12.00

21 - 1

and Raab, 1988; Kolodny and Luz, 1991; Lecuyer et al.,1993, 1996b; Picard et al., 1998; Vennemann and Hegner,1998].[4] Before the Latest Jurassic-Early Cretaceous radiation

of carbonate plankton [Roth, 1989], ectotherm vertebratesliving in surface waters, defined here as about the top 100 mof the water column, can be considered as potential sub-stitutes of paleorecorders of sea surface temperatures [Picardet al., 1998]. To characterize the living depth of Jurassic fish,their d18O values were compared with a previously obtaineddata set of coexisting brachiopods [Picard et al., 1998]. Theoxygen isotope compositions of brachiopods record bottom-water temperatures from the shallowest to the deepest depo-sitional environments of the Anglo-Paris Basin. The oxygenisotope compositions of brachiopods appeared to be in goodagreement with independent hydrodynamic and sedimentarycriteria [Guillocheau, 1991].[5] Well documented sedimentological and paleogeo-

graphic studies of the 600 km � 800 km Anglo-Paris Basin[Ziegler, 1988; Guillocheau, 1991; Robin et al., 2000] andthe high-resolution stratigraphic framework, set up byGarcia et al. [1996], Gaumet et al. [1996] and Garciaand Dromart [1997], may help us to understand changes inthe hydrologic budget and oceanic circulation patterns thataffected its water masses. This Basin was located at tropicallatitudes (20�–30�N) during the Middle and Late Jurassic[Dercourt et al., 1985; Ziegler, 1988] with water depthsdown to about 200 m [Guillocheau, 1991; Picard et al.,1998]. This epicontinental sea, representing the occidentalpart of the equatorial Tethyan ocean, was connected to theopening central Atlantic ocean. Since the middle Bathonian,the development of seaways to the north probably enabledefficient communication of surface waters between theTethyan Basin and boreal realms.[6] The Anglo-Paris Basin, with its high-resolution strati-

graphic framework, thus constitutes an especially interest-ing case study to apply oxygen isotope compositions ofMiddle to Late Jurassic fish tooth enamel to (1) reconstructtropical surface seawater temperature variations with time,(2) document the existence of paleocurrents and theirinfluence on faunal migration at the few million yeartimescale, and (3) explore the consequences of tropicaltemperature variations in terms of sea level variations andthe possible presence of a polar ice cap.

2. Depositional Environments

[7] Depositional environments were dominated by threemain carbonate platform domains (Burgundy, Ardennes andNormandy), Normandy being separated from the two othersby a marly furrow and bordered by land masses during theBathonian and the middle and late Oxfordian (Figure 1).The Callovian is characterized by the drowning of relativelyhigh areas by clayey and sandy wedges with a maximumflooding surface in the middle Callovian [Gaumet et al.,1996]. A regressive-transgressive second-order sequencewas recorded in the late Bajocian to middle Calloviancarbonate series [Guillocheau, 1991; Garcia et al., 1996].This sequence includes (1) a regressive hemicycle from theupper Bajocian to the lower-middle Bathonian boundarycorresponding to an overall infill of the basin by prograda-

tion of carbonate platforms until subaerial exposure, and(2) a transgressive hemicycle from the middle Bathonianuntil the transgressive peak of middle Callovian age (Jasonzone). Siliciclastic sands and silts were deposited at thesame time in southern England and over the Channel(between England and France). The next regressive-trans-gressive cycle corresponds to the progradation of siliciclas-tic (middle Callovian to middle Oxfordian) then carbonatewedges from northwest to southeast.[8] The water depth of the fair weather and storm wave

limits may fluctuate depending on both coastal morphologyand occurrence of submarine topographic breaks. Nonethe-less, these hydrodynamic parameters can be used to definefour main depositional environments in the Anglo-Parisbasin. (1) The protected environment where wave actionis limited by topographic barriers. These environments cansometimes correspond to relatively deep locations comparedto emersive lagoonal environments. Shallow environmentsshow evidence of limited subaerial exposure such as mudcracks or birds’ eyes, but without evaporites (excludingdolomite) or significant siliciclastics. (2) The shorefaceabove the fair weather wave base forms barriers that wereoolitic and skeletal in the Bathonian and Callovian, andwere often made up of reefal mounds in the Oxfordian.(3) The upper offshore located between the fair weather andthe storm wave bases, and (4) the lower offshore occursbelow the storm wave base.

3. Sample Collection

[9] Eighty nine teeth (including seventy eight enamelsand eleven whole teeth) and two bones of Chondrichtyanand Osteichtyan Jurassic fish were selected from shallow todeep marine environments of the Anglo-Paris Basin(Table 1; Figure 1). In addition, eleven bulk teeth and onetooth enamel of reptiles, mainly marine crocodilians, wereselected when found associated with fish teeth. Vertebrateremains were sampled along sedimentary isochron profiles[Garcia et al., 1996; Gaumet et al., 1996] with a resolutionof about 1 Myr from the Bajocian to the Tithonian, with oneAalenian tooth. Isochrons consist of sedimentary bedsdefined by monospecific or plurispecific brachiopod asso-ciations that are laterally continuous throughout the basinand coincide with maximum platform floodings [Garciaand Dromart, 1997]. These brachiopod shell beds wereaccurately identified on the basis of one hundred and fortyexploratory oil wells that were used to construct highfrequency cycle correlations [Garcia and Dromart, 1997].They were also calibrated with ammonite standard zonationand Jurassic timescale [Gradstein et al., 1994].[10] Chondrichtyan fish are sharks represented by four

main genera that are Asteracanthus (crushing fish),Notidanus, Sphenodus and Odontaspis (tearing fish).Asteracanthus feeds on shells and is characterized by platyand massive teeth with an enamel structure [Cuny, 1998].Jurassic Osteichtyan fish are represented by durophageousfish, Pycnodontidae with tabular teeth, except one genus,Sphaerodus, having hemispherical teeth, and Gyrodontidae(Gyrodus). Ecology and, especially, living depths of Juras-sic fish, cannot simply be determined from paleontologicalor paleoenvironmental criteria. Depositional environments,

21 - 2 LECUYER ET AL.: TEMPERATURES OF JURASSIC SEAWATER

Figure 1. Sampling locations of Jurassic fish and reptile remains. The size of open circles isproportional to the number of sites. Biogenic phosphates were selected from the western (Normandy,Boulonnais, south England) and the eastern (Burgundy, Jura, and southeast basin) parts of the Anglo-Paris Basin. The paleogeographic map (modified after Dercourt et al. [1985] and Ziegler [1988]) showsthat Western Europe occupied a tropical position during the Middle-Late Jurassic; a latitude is shown andlabelled 20�–30� to give an estimate of uncertainties. Since the Bathonian, the Anglo-Paris basin, locatedat the occidental extremity of the Tethys, was connected northward to boreal realms. North-southseaways, formed during the initial rifting phases of the North Sea, were generally filled by shallowmarine (early-middle Bathonian), then by deeper marine deposits (late Bathonian). Abbreviations are asfollows: B, Boulonnais; N, Normandy; P, Poitou.

LECUYER ET AL.: TEMPERATURES OF JURASSIC SEAWATER 21 - 3

Table

1.Oxygen

IsotopeCompositionsofAalenianto

PortlandianVertebrate

Phosphates

AlongWithTaxonDetermination,Sam

ple

Locations,Ages,andEnvironmentsa

Vertebrate

Taxa

Code

Sam

ple

Stratigraphic

Age

AmmoniteZones

Isochron

Age,

Myr

Location

Depositional

Environments

d18O,

%P205,

%

Odontapsis

93399

T-e

Aalenian

Concavum

Concavum

177.1

Cu

Hte

Saone-Coulevon

O19.3

43

Asteracanthus

D66b

T-e

E.Bajocian

Sauzei

Sauzei

174.3

St

Var-Sollies-Toucas

UO

18.7

41

Pycnodus

L9b

T-e

M.Bajocian

Humphriesianum

Humphriesianum

173.2

Se

Saoneet

Loire-Sennecey

UOPZ

20.5

44

Oxyrhina

L12

T-b

M.to

L.Bajocian

Humphriesianum

Humphriesianum

172

Li

Saoneet

Loire-StSorlin

UOPZ

19.5

37

Pycnodus

93401b

T-e

M.Bajocian

Humphriesianum

Humphriesianum

172

Li

Saoneet

Loire-Laives

UOPZ

19.9

44

Fish

D28

BL.Bajocian

Acris

Acris

170.2

Po

Cote

d’O

r-Pouillenay

UOpPZ

14

28

Asteracanthus

L10b

T-e

L.Bajocian

Acris

Acris

170.2

HSaoneet

Loire-Hurigny

UOBPZ

20.1

34

Marinereptile

L11

T-b

L.Bajocian

Acris

Acris

170.2

HSaoneet

Loire-Hurigny

UOBPZ

17.5

30

Hybodus

O1

T-b

L.Bajocian

Parkinsoni

Parkinsoni

169.3

OCalvados-Omahabeach

UO

21.2

29

Pycnodont

D111-p

bT-e

E.Bathonian

Convergens

Convergens

169.1

Bn

Var-Bandol

UO

19.7

38

Asteracanthus

93357b

T-e

E.-M.Bathonian

Progracilis

Globata

167.9

SStonesfield(U

K)

P20.5

33

Crocodylian

93369

T-b

E.-M.Bathonian

Progracilis

Globata

167.9

SStonesfield(U

K)

P20.8

28

Asteracanthus

D109-A

bT-e

E.-M.Bathonian

--

-Vy

Cher-Vallenay

S19.4

42

Asteracanthus

AST53b

T-e

E.-M.Bathonian

Progracilis-Subcontractus

Globata-Multiplicata

167.9

Me

Jura-M

erey

s/Montrond

P18.7

35

Asteracanthusc

D6b

T-e

M.Bathonian

Progracilis-Subcontractus

Globata-Multiplicata

167.6

VCote

d’O

r-Vanvey

S19.7

35

Asteracanthus

D103-p

bT-e

M.Bathonian

--

-Gl

Gloucester

(UK)

S19.8

35

Asteracanthus

AST54b

T-e

M.-L.Bathonian

Hodsoni-Subcontractus

Concinna-Multiplicata

166.8

Na

Ain-N

antua

LO

19.6

33

Notidanus

93365Nb

T-e

M.-L.Bathonian

Hodsoni

Concinna

166.4

Tr

Isere-Trept

UOp

19.4

32

Pycnodont

93365Pb

T-e

M.-L.Bathonian

Hodsoni

Concinna

166.4

Tr

Isere-Trept

UOp

19.4

39

Asteracanthus

P6-e

bT-e

M.-L.Bathonian

Hodsoni-Retrocostatum

Concinna-Digona

166.4-165.3

Au

Aisne-Aubenton

SPE

20.4

35

Mesodon

P1b

T-e

M.-L.Bathonian


Concinna-Digona

166.4–165.3

Ra

Calvados-Ranville

UOPZ

21

45

Asteracanthus

P3-e

bT-e

M.-L.Bathonian


Concinna-Digona

166.4–165.3

Ma

Sarthe-Mam

ers

S/UOPZ

19.9

42

Asteracanthus

P13b

T-e

M.-L.Bathonian


Concinna-Digona

166.4–165.3

Mr

Pas-de-Calais-Marquise

S20.6

37

Machimosaurusb.

92210

T-b

L.Bathonian

post-H

odsoni

postConcinna

<166.4

Ga

Indre-StGaultier

P19.4

40

Asteracanthus

93362b

T-e

L.Bathonian

post-H

odsoni

postConcinna

<166.4

Ga

Indre-StGaultier

P20.3

37

Asteracanthus

SERA-e

bT-e

L.Bathonian

Retrocostatum

Digona

165.3

Nu

Cote

d’O

r-NuitsSt.Georges

protected

20.2

36

Asteracanthus

93360b

T-e

L.Bathonian

post-Retrocostatum

post-D

igona

<165.3

WWiltshire(U

K)

P(bay)

20.5

30

Asteracanthus

D71b

T-e

L.Bathonian

justeante

Discus

ante

Eudesia

<164.6

Lq

Pas-de-Calais-Locquinghen

UOPZ

21.7

42

Asteracanthus

P12b

T-e

L.Bathonian

ante

Discus

ante

Eudesia

164.6

Mr

Pas-de-Calais-Marquise

UOPZ

22.3

40

Asteracanthus

Ja1b

T-e

L.Bathonian

Discus

Eudesia

164.6

JaYonne-Jaulges

LO

20.3

40

Asteracanthusc

D21Ab

T-e

L.Bathonian

Discus

Eudesia

164.6

LP

Cote

d’O

r-Les

Perrieres

LO

19.1

34

Pycnodontc

D19b

T-e

L.Bathonian

Discus

Eudesia

164.6

LP

Cote

d’O

r-Les

Perrieres

LO

18.8

35

Pycnodontc

D21Pb

T-e

L.Bathonian

Discus

Eudesia

164.6

LP

Cote

d’O

r-Les

Perrieres

LO

18.7

34

Asteracanthus

D35b

T-e

L.Bathonian

Discus

Eudesia

164.6

Ri

Boulonnais-Rinxent

LO

21.3

37

Asteracanthus

Be-1Ab

T-e

L.Bathonian

Discus-Bullatus

Eudesia-D

ivio

164.6–163.9

Me

Hte

Saone-Merey

S19.1

38

Asteracanthus

Bib

T-e

E.Callovian

Bullatus

Divio

163.9

Bi

Yonne-Brion

S20.2

35

Asteracanthusc

D25b

T-e

E.Callovian

Bullatus

Divio

163.9

DCote

d’O

r-Dijon

UOPZ

19.6

34

Asteracanthus

AST55b

T-e

E.Callovian

Bullatus

Divio

163.9

La

Cote

d’O

r-Ladoix

UOPZ

19.0

36

Fish

D22

T-b

E.Callovian

Koenigi

Kalli

163.3

Ta

Cote

d’O

r-Talant

P17.5

33

Asteracanthus

Be-2Ab

T-e

E.Callovian

Koenigi

Kalli

163.3

Or

Doubs-Ornans

UOPZ

19.6

39

Crocodylian

D8

T-b

E.Callovian

Calloviense

Torqui

162.2

ECote

d’O

r-Etrochey

UOPZ

16.6

34

Pycnodusc

D11ab

T-e

E.Callovian

Calloviense

Torqui

162.2

ECote

d’O

r-Etrochey

UOPZ

20.0

37

Asteracanthusc

D10b

T-e

E.Callovian

Calloviense

Torqui

162.2

ECote

d’O

r-Etrochey

UOPZ

18.8

35

Metriorhynchus

N2

T-b

E.Callovian

Calloviense

Torqui

162.2

Ba

Calvados-Bavent

OBPZ

19.3

39


Table

1.(continued)

Vertebrate

Taxa

Code

Sam

ple

Stratigraphic

Age

AmmoniteZones

Isochron

Age,

Myr

Location

Depositional

Environments

d18O,

%P205,

%

Asteracanthus

L6-e

bT-e

M.Callovian

Jason

Orbignyana

161.5

At

Hte

Saone-Authoison

UOBPZ

19.1

37

Asteracanthus

M2b

T-e

M.Callovian

Coronatum

Oxoniensis

161.1

Pi

Vienne-Carrieredes

Lourdines

?19.8

43

Notidanus

A1-L

T-b

M.Callovian

Coronatum

Oxoniensis

161.1

-Wallucke(D

)LOBPZ

17.7

18

Asteracanthus

D37b

T-e

M.Callovian

Coronatum

Oxoniensis

161.1

ECote

d’O

r-Etrochey

UOBPZ

19.2

34

Asteracanthus

P2b

T-e

L.Callovian

Athleta

Athleta

160.3

Mi

Vendee-St.Michel

enl’Herm

OBPZ

20.8

34

Asteracanthus

D36b

T-e

L.Callovian

Athleta

Athleta

160.3

Pr

Cote

d’O

r-Pruslys/ource

UOBPZ

18.9

39

Asteracanthus

D27b

T-e

L.Callovian

Athleta

Athleta

160.3

Ta

Cote

d’O

r-Talant

UOBPZ

19.5

30

Gyrodus

P5

T-b

L.Callovian

Athleta

orLam

berti

Athleta

orLam

berti

160.3–153.6

Mb

Sarthe-Marolles

lesBraults

UOBPZ

20.3

41

Sphenodus

93355

T-e

L.Callovian

Athleta

orLam

berti

Athleta

orLam

berti

160.3–153.6

Vo

Ardeche-LaVoulte

UOdBZP

19.5

11Marinereptile

93405

T-b

L.Callovian

Athleta

orLam

berti

Athleta

orLam

berti

160.3–153.6

Vi

Calvados-Vaches

noires

UOBZP

21.7

38

Fish

N3

BL.Callovian

Athleta

orLam

berti

Athleta

orLam

berti

160.3–153.6

Vi

Calvados-Villers-sur-mer

LOBPZ

20.3

27

Marinereptile

93404R

T-b

L.Callovian

Lam

berti

Lam

berti

159.6

At

Hte

Saone-Authoison

LOBPZ

18.7

28

Odontaspisl.

L41-e

bT-e

L.Callovian

Lam

berti

Lam

berti

159.6

At

Hte

Saone-Authoison

LOBPZ

20.7

44

Notidanusm.

L126-b

T-b

L.Callovian

Lam

berti

Lam

berti

159.6

At

Hte

Saone-Authoison

LOBPZ

19.4

42

Asteracanthus

W46b

T-e

L.Call-E.Oxf.

--

159.4

Vd

Vaud-Villeneuve

?20.5

36

Asteracanthus

D39b

T-e

E.Oxfordian

Mariae

Mariae

159.1

-Woodham

(UK)

?19.1

43

Notidanusm.

L5-b

T-b

E.Oxfordian

Cordatum-M

ariae

Cordatum-M

ariae

158.8

Ty

Jura-LaBillode

O18.4

16

Asteracanthus

Be-3Ab

T-e

E.Oxfordian

Cordatum-M

ariae

Cordatum-M

ariae

158.8

Or

Doubs-Ornans

O20.9

42

Asteracanthus

P11

bT-e

E.Oxfordian

Cordatum

Cordatum

158.5

To

Calvados-Trouville

s/mer

UOBPZ

20.6

22

Asteracanthus

L3b

T-e

E.Oxfordian

Cordatum

Cordatum

158.5

Ty

Jura-Pontdudiable

O20.4

34

Lam

nidae

B5L-e

bT-e

E.Oxfordian

Cordatum

Cordatum

158.5

Ue

Jura

suisse-U

ken

(CH)

LOBPZ

21.5

33

Notidanusm.

93402-N

-eb

T-e

E.Oxfordian

Cordatum

Cordatum

158.5

Ty

Doubs-Tarcenay

O20.7

44

Odontaspisl.

93402-O

bT-e

E.Oxfordian

Cordatum

Cordatum

158.5

Ty

Doubs-Tarcenay

O19.4

28

Reptile

D32

T-b

E.Oxfordian

Cordatum

Cordatum

158.5

Ar

Jura-A

rcs/Montenot

O18.7

34

Notidanuss.

W22-b

T-b

E.Oxfordian

Cordatum

Cordatum

158.5

Mf

Jura-M

ontfaucon(CH)

O20.3

20

Pycnodus

P15pb

T-e

M.Oxfordian

--

-Gn

Cote

d’O

r-Gigny

OBPZ

20.9

37

Reptile

P15R-e

T-e

M.Oxfordian

--

-Gn

Cote

d’O

r-Gigny

OBPZ

19.3

40

Marinereptile

L14

T-b

M.Oxfordian

Plicatilis

Plicatilis

157.8

FHte

Marne-Foug

UO(PZ)

20.8

32

Sphenodussp.

R1b

T-e

M.Oxfordian

Plicatilis-Antecedens

Plicatilis-Transversarium

157.8–157.6

Vo

Ardeche-Ravin

duCheynier

UOdBZP

20.8

45

Pycnodont

D100-p

bT-e

M.Oxfordian



157.8–157.6

-Yorkshire-(U

K)

S20.5

40

Pycnodontidae

B3pb

T-e

M.Oxfordian

Transversarium

Transversarium

157.6

UJura-StUrsanne(CH)

UOPZ

21.4

37

Sphenodusl.

93398-e

bT-e

M.Oxfordian

Transversarium

Transversarium

157.2

Cr

Ardeche-Crussol

UOdBZP

21

36

Sphaerodussp.

D70b

T-e

M.Oxfordian

Transversarium

Transversarium

156.6

Ta

Cote

d’O

r-Talant

LOBPZ

21.5

45

Lam

niform

B4L-e

bT-e

M.Oxfordian

Transversarium

Transversarium

156.9

Si

Jura-Siblingen

(CH)

UOBPZ

21.1

27

Pycnodont

D106-p

bT-e

M.-L.Oxfordian

Transversarium-Bifurcatus

Transversarium-Bifurcatus

156.9–155.9

Vn

Meuse-Verdun

P21.2

42

Pycnodus

P16b

T-e

L.Oxfordian

Bifurcatus

Bifurcatus

155.9

Ml

Yonne-Maillyle

Chateau

UOPZ/S

20.6

40

Sphenodusl.

L1-d

T-b

L.Oxfordian

Bifurcatus

Bifurcatus

155.9

Ch

Jura-Chatelneuf

OBPZ

18

34

Sphenodusl.

L1-e

bT-e

L.Oxfordian

Bifurcatus

Bifurcatus

155.9

Ch

Jura-Chatelneuf

OBPZ

20.8

37

Sphenodusl.

L8-d

T-b

L.Oxfordian

Bifurcatus

Bifurcatus

155.9

Sa

Jura-Savigna

OBPZ

18.9

33

Sphenodusl.

L8-e

bT-e

L.Oxfordian

Bifurcatus

Bifurcatus

155.9

Sa

Jura-Savigna

OBPZ

20.6

37

Pycnodontc

L13b

T-e

L.Oxfordian

Bifurcatus

Bifurcatus

155.9

PMeurtheet

Moselle-Pagny

P20.6

34

Asteracanthus

93363b

T-e

L.Oxfordian

Bifurcatus

Bifurcatus

155.9

He

Calvados-Hennequeville

UO

18.5

31


constituting a condensed image of fauna and flora activityoccurring from surface to bottom waters, also cannotprovide information on living depths in the water column.Previous studies, however, indicate that pycnodont fishhave been mostly marine, and only in some cases estuarineto freshwater dwellers [Martill, 1990; Nursall, 1996;Poyato-Ariza et al., 1998]. Pycnodonts must have been animportant component of tropical and subtropical coral reefcommunities, analogous to balistid fish in modern oceans[Nursall, 1996]. Asteracanthus sharks are considered asbeing essentially marine, but their ecology is poorly known[Cappetta, 1987]. Other sharks, with lamniform teeth, wereprobably piscivorous [Cappetta, 1987; Martill, 1990].[11] Enamel is more resistant than dentine or bone to post-

depositional oxygen isotope exchange [e.g., Sharp et al.,2000] because of its high degree of mineralization, thereforethis phosphatic tissue was preferentially selected and sepa-rated mechanically with a microdrill under a binocular(Table 1). In the case of the smallest teeth, a few bulkisotopic analyses were performed because it was not possi-ble to separate enough enamel.[12] Similarly, carbonate ions that are present in the apatite

structure are supposed to be less resistant than phosphateions to oxygen isotope exchange during diagenetic alteration[Iacumin et al., 1996;McArthur and Herczeg, 1990]. To testthe state of preservation of Jurassic teeth, we have measuredthe oxygen isotope compositions of both phosphate andcarbonate in fifteen fish and six reptile teeth.

4. Analytical Methods

[13] Carbonate apatite samples were first treated with a3% sodium hypochlorite solution for 4 hours to removeorganic matter and rinsed three times with distilled water.Then they were treated with a 1M acetic acid-acetate bufferfor two days to remove exogenous carbonates according tothe method presented by Bocherens et al. [1996]. Oxygenand carbon isotope ratios from the carbonate in substitutionin the apatite were determined using the phosphoric acidmethod [McCrea, 1950] with a reaction time of 48 hours at30�C. Reproducibility for carbon and oxygen isotopemeasurements in carbonates were ±0.05% and ±0.1%,respectively.[14] Phosphate radicals were isolated from biogenic apa-

tites as Ag3PO4 crystals using the method of Crowson et al.[1991] modified by Lecuyer et al. [1993]. Silver phosphatewas reacted with graphite at 1100�C to produce pure CO2

[Lecuyer et al., 1998] (modified after O’Neil et al. [1994]).The quality of the reaction, marked by the absence of COproduction, was monitored by the carbon isotope composi-tion of CO2 derived from the graphite (Figure 2a). Carbondioxide was analyzed with a VG Prism2 mass spectrometer.All data are quoted in the d notation relatively to SMOW,via calibration on NBS18 and NBS19 international stand-ards. Several tooth enamels, including all those with ex-treme d values were duplicated. Repeated analyses of thephosphorite NBS120c gave a mean d18O value of 21.68 ±0.19% (Figure 2b). The CO2 gave a mean d13C value of�23.51 ± 0.11% (Figure 2c), similar to that of graphiteanalyzed by the CuO method (d13C = �23.5 ± 0.05%). TheP2O5 contents of samples were calculated from their chem-T

able

1.(continued)

Vertebrate

Taxa

Code

Sam

ple

Stratigraphic

Age

AmmoniteZones

Isochron

Age,

Myr

Location

Depositional

Environments

d18O,

%P205,

%

Pycnodont

B1p-e

bT-e

L.Oxfordian

Bim

ammatum

Bim

ammatum

155.2

Ga

Jura-G

achlingen

(CH)

UOBPZ

20.5

38

Asteracanthusc

93364b

T-e

L.Oxfordian

Planula

Planula

154.4

TYonne-Tonnerre

UOZP

19.7

36

Teleosaurides

92154

T-b

L.Oxfordian

Planula

Planula

154.4

TYonne-Tonnerre

UOZP

16.5

33

Microdon

D108-p

bT-e

L.Oxfordian

Planula

Planula

154.4

TYonne-Tonnerre

UOpPZ

20

47

Asteracanthus

P19b

T-e

L.Oxf.to

E.Kim

.Planula

toCymodoce

Planula

toCymodoce

155.2–152.3

Mc

Saone&

Loire-Flace

Macon

P/UOPZ

19.7

42

Peloneustes

W19

T-b

E.Kim

meridgian

--

154.1–152.6

Ha

Seinemaritim

e-LeHavre

O20.7

34

Sphaerodussp.

W29

T-e

E.to

L.Kim

meridgian

--

-Ne

Jura-LaNeuveville

(CH)

P/UOPZ

22

41

Pycnodont

D69

T-e

Kim

meridgian

--

-Gr

Hte

Saone-Arc-les

Gray

?21.3

44

Pycnodont

D33b

T-e

L.Kim

meridgian

MutabilisorEudoxus

MutabilisorEudoxus

152.3–151.4

Do

Aube-Dolancourt

UOpPZ

20

39

Sphaerodussp.

W26b

T-e

L.Kim

meridgian

--

152.6–150.7

Vd

Vaud-Ste

Croix

(CH)

UOpPZ

21.4

43

Pycnodont

D107-p

bT-e

E.Tithonian

Gigas

Gigas

150.2

Bo

Aube-Bourguignons

UOpPZ

20.8

41

Sphaerodussp.

D45b

T-e

E.Tithonian

Gigas

Gigas

150.2

Mt

Haute

Saone-Mantoche

UOpPZ

20.7

37

Mesodongigas

D46b

T-e

E.Tithonian

Gigas

Gigas

150.2

Mt

Haute

Saone-Mantoche

UOpPZ

20.1

42

Sphaerodussp.

D68b

T-e

E.Tithonian

Gravesiana

Gravesiana

150.2

No

Haute

Saone-Noiron

UOpPZ

20.4

43

Pycnodus

93396b

T-e

Portlandian

--

144.2–145.6

Sl

Soleure

(CH)

?20.0

44

Pycnodusgigas

Be5-p

bT-e

Portlandian

--

144.2–145.6

Cx

LaChauxdefonds(CH)

?21.1

42

Mesodongigas

93471

T-e

Portlandian

--

144.2–145.6

Vl

Doubs-Villers

-le-lac

?20.6

24

aNotethatMicrodon,Mesodon,PycnodusgeneraareallPycnodontidae.Stratigraphicages

forisochronswerereported

ontheam

monitebiostratigraphicscaleandontheabsolutescaleproposedbyGradsteinet

al.[1994].P2O5wt%

ofbiogenicapatites

werecalculatedconsideringameanvalueof80±3%

forthesilverphosphatechem

icalyieldobtained

withNISTNBS120c.Depositionalenvironments:P,protected;S,=

shoreface;O,offshore;U,upper;L,lower;PZ,photiczone;

BPZ,below

photiczone;

p,proxim

al;d,distal.Sam

ples:B,bone;

T,tooth;b,bulk;d,dentine;

e,enam

elloıd.

bValues

usedin

Figure

5.

cDatathat

werepreviouslypublished

inthework

ofPicard

etal.[1998].


ical phosphate yields using the average yield of 80 ± 3%obtained for the NBS120c phosphorite that contains 33.33%of P2O5 (Table 1).[15] Diagenetic alteration of fossil apatite was detected in

eleven samples during the chemical procedures using thefollowing criteria: (1) recovery of silver phosphate down to60% (Table 1), because of the replacement of phosphates bycarbonates, silica or metal oxides (samples A1-L, 93355,L5b, 93471), (2) solutions that turned from red to yellowduring neutralization with KOH (O1, N3, D22, 93355,D28), revealing the presence of metal oxides (Fe, Mn,Al), and (3) both low d18O values of PO43� and d13Cvalues of graphite (Figure 2a) for samples L11, 92154, D8and D28, indicating the presence of exotic organic mole-cules that were not totally eliminated during the wetchemical procedures [Lecuyer, 2003].

5. Results

[16] Oxygen isotope compositions of phosphate fromJurassic fish and reptiles are reported in Table 1. Analysesof associated dentine and enamel from two teeth of Chon-drichtyan lamnidae (samples L8 and L1) gave chemicalphosphate yields that are about 10% lower for the dentinethan for the enamel. The dentine has d18O values from 1.7 to2.8% lower than the enamel (Table 1), which indicatesstrong isotopic disequilibria between the two coexistingphosphatic tissues. Similar observations were made bySharp et al. [2000] and Puceat et al. [2003]. Massiveenamel of Asteracanthus and pycnodonts have high meanP2O5 percentages with relatively low variance (36.7 ± 3.6%and 39.3 ± 3.4%, respectively), bracketing those obtainedon enamels from tearing teeth (38.2 ± 6.8%; n = 13) thathave a microstructure close to that of modern lamnidae. Bycontrast, bulk fish teeth and bones have variable and lowP2O5 contents (31.6 ± 6.9%) and constitute a fossil materialthat commonly suffered chemical and isotopic alterations.[17] The range and mean d18O values of all well-preserved

vertebrate taxa (where no indicators of diagenesis wereobserved) are reported in Table 2. Similar ranges andmean d18O values were obtained with Asteracanthus andPycnodontidae enamels from the Bathonian-Callovian(19.5 ± 0.5 and 19.6 ± 0.7%) and Oxfordian-Tithonian(20.1 ± 0.6 and 20.7 ± 0.5%) periods. Mean d18O valuesfor other vertebrates like Notidanus (20 ± 0.7%) andOdontaspis (20 ± 0.7%) sharks, though based on a verylimited number of samples, have similar values to thosedocumented for Asteracanthus and Pycnodontidae. Meand18O values for Chondrichtyan Sphenodus (20.8 ± 0.2%)and Osteichtyan Sphaerodus (21.2 ± 0.6%) are higherthan those for Asteracanthus and Pycnodontidae sensustricto, but they are mainly restricted to the Late Jurassic,a period characterized by higher d18O values than thosedocumented throughout the Middle Jurassic. The morepositive d18O values for Sphenodus and Sphaerodus mayindicate that they lived in deeper waters and do not recordsurface temperatures unlike Asteracanthus seems to do(Figure 3). However, we note that Pycnodontidae haved18O values indistinguishable from those of Asteracanthusduring the Bathonian-Callovian and they constitute the

most abundant fossil fauna analyzed during the Oxfor-dian-Tithonian period (Table 2). Therefore the high d18Ovalues of Oxfordian fish teeth can be considered as alsorecording the temperature of the upper part of the watercolumn.[18] Mean d18O values of middle Bathonian to late

Callovian (168–160 Myr) Asteracanthus have been cal-culated for the various depositional paleoenvironmentsdocumented in the eastern part of the Basin (Figure 3).Note the uniformity of the d18O values of Asteracanthusteeth (from 19.2 ± 0.2 to 19.7 ± 0.6%) that are preservedin inner to outer depositional environments. Middle to lateBathonian samples from the western and northwestern partof the basin (Boulonnais, Normandy, and Poitou regions)have d18O values that are on average 1.5% higher than theirsoutheastern counterparts (Table 1). Samples from thecentral region (Ja1, Bi, SERA, Table 1) have intermediateoxygen isotope ratios, confirming the existence of anisotopic gradient across the whole basin.[19] The Bajocian to the Tithonian fish tooth samples

from the eastern part of the basin show d18O variations over20 Myr (Figure 4). These isotopic variations define anenvelope from 0.5 to 1.5% wide for the various isochrons.This isotopic range is comparable to the one measured byVennemann et al. [2001] on recent fish teeth, which istypically between 0.6 and 1.1% for different teeth from asingle shark. This naturally occurring variation in oxygenisotope compositions recorded in fish teeth may reflect thediversity of the living environments which includes:(1) thermal gradients within the water column; (2) seasonalthermal variations since the growth of a fish tooth representsless than a year (several weeks to several months dependingon species), but they should remain limited under tropicallatitudes; (3) coastline proximity and the influence of fresh-water inputs; and (4) the possible occurrence of surficialoceanic currents.[20] Three major stages may be distinguished: (1) a

period of decreasing d18O values from 20 to 19% for theBajocian to Bathonian interval, (2) a rapid increase of d18Ovalues up to 21% initiated during the late Callovian andreaching a maximum during the early-middle Oxfordian,and (3) another stage of decreasing d18O values, similar inamplitude to stage 1, starting in the late Oxfordian to reachvalues of 20% around the Oxfordian-Kimmeridgianboundary.[21] Oxygen isotope compositions of carbonates from

Jurassic fish teeth range from 24.5 to 30.0% whilst thoseof reptiles range from 23.6 to 30.4% (Table 3). For fishteeth, differences between the d18O values measured inapatite carbonate and its associated phosphate oxygen(Dc-p) range from 7.0 to 9.5%, except for two samples; awhole tooth (L12; Dc-p = 5.0%) and one altered sample(93355; Dc-p = 5.7%). These values are within or close tothe known fractionations (Figure 5) between apatite carbon-ate and phosphate oxygen [Longinelli and Nuti, 1973;O’Neil et al., 1969; Iacumin et al., 1996].[22] The amount of carbonate substituted in the apatite

structure of Jurassic fish tooth enamel ranges from 3.9 to5%, except for samples D21P and 93357 (Table 3). Thesevalues match those of 4–5% that were measured in present-



day vertebrate teeth [LeGeros and LeGeros, 1984; Michel etal., 1995]. The bulk tooth L12 has a low CO3

2� content of2.9% and a low Dc-p of +5 both diagnostics of a diageneticalteration of the carbonate component of the apatite. Thereptile bulk teeth have CO3

2� contents that range from 3.8to 7%.

6. Discussion

6.1. Diagenetic Perturbations

[23] We conclude from our observations during the chem-ical procedures that seven vertebrate whole teeth (i.e., <8%of the enamel samples) and the two fish bone fragmentshave been chemically and isotopically modified by diage-netic processes. Only one enamel from a Sphenodus tooth(93355) and one enamel from a massive tooth (93471) aresuspect on the basis of the selected criteria. Some of thesephosphate samples are depleted in 18O relative to coexisting

or associated enamel (D28; D22; A1-L; Table 1). Moreover,only two fish teeth (enamel 93355 and whole tooth L12)plot outside the domain of apparent oxygen isotopic equi-librium between phosphate and carbonate, limited by pre-viously proposed fractionation equations (Figure 5). Thissuggests that most enamels from Jurassic teeth have con-served their primary isotopic signatures.[24] On the basis of oxygen isotope analyses of modern

teeth, dentines are depleted in 18O by up to 1.7% relative toassociated enamel [Vennemann et al., 2001]. For compari-son, Jurassic dentines from two lamniform teeth show d18Ovalues up to 2.8% lower than coexisting enamel, suggestingthat these dentines have been significantly altered. Conse-quently, we do not consider bulk samples for paleoenvir-onmental studies even if some of them have d18O values inthe range of contemporaneous fish enamel (W22-b, L126-b,L12; Table 1). The greater resistance of Jurassic enamels todiagenetic processes than either dentine or bone supports

Figure 2. (opposite) Stable isotope compositions of CO2 from Ag3PO4 of Jurassic apatites and phosphorite standardNBS120c. (a) d13C and d18O values of CO2 from Ag3PO4 of Jurassic apatites after reaction with graphite at 1100�C. Notethat most samples having d13C values close to the lower limit of the envelope (defined with 2s a 95% of confidence level)were diagenetically altered (*), except D45, d100p, and Be-1A (see text for more explanations). (b and c) Frequencyhistograms of carbon and oxygen isotope compositions of CO2 from repeated analyses of the phosphorite NBS120c afterreaction of silver phosphate with graphite at 1100�C. The small standard deviations for O and C, of 0.19% and 0.11%respectively, indicate that oxygen from silver phosphate was converted into CO2 without significant production of CO[Lecuyer, 2003].

Figure 3. Mean d18O values calculated for the studied collection of Asteracanthus sharks through theBathonian-Callovian interval. Oxygen isotope compositions are reported along a general depositionalenvironment profile (modified from Gaumet et al. [1996]). Environments were defined by hydrodynamiclimits that are the fair weather base (FWB), the storm wave base (SWB), and by the occurrence ofphotosynthetic organisms (PZB = base of the photic zone). Note the relative constancy withinuncertainties of sharks’ d18O values with deepening of the basin, thus indicating that they record seasurface temperatures.


earlier studies realized on Mesozoic vertebrate teeth[Kolodny et al., 1996; Sharp et al., 2000].

6.2. Vertebrate D18O Values and Sea Surface

Temperatures

[25] Oxygen isotope analysis of apatite from modernselachians has shown that isotopic temperatures reflect theaverage temperature of the seawater layer in which the fishlives [Picard et al., 1998]. Although the living depths ofJurassic vertebrate taxa are not known, estimates can be

made. Marine bottom temperatures can be derived from thed18O values of brachiopods giving a lower limit for thewater column [Picard et al., 1998]. Isotopic temperaturesinferred from the d18O values of brachiopods sampled fromknown different depositional environments can be comparedwith the temperatures derived from the associated vertebrated18O values. Note that if the vertebrates and brachiopodswere living at the same time and place (associated fossils),they were not necessarily present in the same water layer.[26] Mean d18O values, calculated for both middle Batho-

nian to late Callovian Asteracanthus sharks from the easternpart of the Anglo-Paris basin, are reported in Figure 3 as afunction of their depositional environment. The isotopicvalues, ranging from 19.2 ± 0.2 to 19.7 ± 0.6%, remainrelatively constant independent of the deepening of themarine basin from the shoreface to lower offshore environ-ments at about 200 m depth. This pattern of isotopicdistribution strongly contrasts with the d18O values ofcoexisting brachiopods that increase with depth and recordthermal differences of up to 12�C between surface andlower offshore bottom waters [Picard et al., 1998]. Theseobservations suggest that the oxygen isotope compositionsof Asteracanthus sharks record temperatures close to seasurface temperatures.[27] Isotopic temperatures are calculated from the frac-

tionation equation determined by Kolodny et al. [1983] onthe basis of various fresh and seawater fish species. Asimilar equation (Figure 6) is deduced from present-day

Table 2. Statistics of Mean d18O Values Calculated for Dental

Apatite From Asteracanthus, Pycnodont, and Sphenodus for the

Bathonian-Callovian and Oxfordian-Tithonian Ontervals

Period/FaunaAsteracanthus,

n = 19Pycnodont,

n = 7Sphenodus,

n = 1

Bathonian-CallovianMean 19.48 19.57 19.50Standard deviation 0.51 0.65 0.00Minimum 18.70 18.70 19.50Maximum 20.30 20.50 19.50

Asteracanthus,n = 7

Pycnodont,n = 11

Sphenodus,n = 4

Oxfordian-TithonianMean 20.13 20.71 20.80Standard deviation 0.64 0.47 0.16Minimum 19.10 20.00 20.60Maximum 20.90 21.40 21.00

Figure 4. Variations of d18O values of fish tooth enamel from the Bajocian-Tithonian of the Anglo-Parisbasin. Fish teeth were sampled on isochrons with an approximate resolution of 1 Myr. During theBathonian, fish samples from the northwestern part of the Anglo-Paris basin define a colder water mass(dashed area) in comparison to contemporaneous samples from the southern eastern part. The appearanceof boreal ammonites Cardioceratidae during the late Callovian-middle Oxfordian is synchronous with anincrease in fish tooth d18O values. Open squares indicate fish samples coming from protected and poorlycontrolled environments.


shark and water isotopic data published in the work ofPicard et al. [1998].[28] Assuming a d18O value of 0% compatible with both

the absence of continental ice caps and the high-salinity oflow-latitude surface sea waters, isotopic temperatures of 27to 29�C are calculated, and are comparable to surfacetemperatures measured in modern tropical platform waters[Adlis et al., 1988]. Similar d 18O values, and thereforeisotopic temperatures, of contemporaneous sharks (Astera-canthus, Notidanus, Odontaspis and Sphenodus) and Pyc-nodontidae (Tables 1 and 2) strongly suggest that these fishwere principally restricted to surface waters. They are usedto reconstitute sea surface temperatures.

6.3. Basin-Scale Oxygen Isotope Variations

[29] Three different interpretations may be formulated toexplain the d18O spread of 3% identified throughout theAnglo-Paris basin from the Middle to Late Jurassic. In termsof salinity changes, it would correspond to variations of up to7.5 ppt over the basin, assuming a 2.5 ppt salinity increase for1% increase of d18O value of seawater under subtropicallatitudes [Craig and Gordon, 1965]. Such salinity gradientsseem unrealistically large without any known physicalbarrier isolating the western part of the basin from the east.

Figure 5. d18O measurements of phosphate tooth enamel and structural carbonate from Jurassic fishapatites of the Anglo-Paris Basin. Previously proposed fractionation equations between phosphate andcarbonate are also reported: 1, Longinelli and Nuti [1973] and O’Neil et al. [1969]; 2, Iacumin et al.[1996]. Except for two undetermined chondrichtyan teeth, Jurassic Asteracanthus and pycnodontidae fallbetween the two curves of oxygen isotope fractionation.

Table 3. Oxygen Isotope Compositions and Mass Fractions of

Structural Carbonate From a Selection of Fish and Reptile Apatites

Sample Code d18O(CO3) D(CO3-PO4) CO3, wt %

FishL13 (T-e) 29.1 8.5 nda

93364 (T-e) 27.6 7.9 5.293355 (T-e) 25.2 5.7 n.d.D27 (T-e) 28.4 8.9 n.d.D10 (T-e) 26.7 7.9 n.d.D25 (T-e) 26.6 7.0 4.7D11a (T-e) 27.2 7.2 3.993362 (T-e) 28.6 8.3 4.8D21A (T-e) 27.7 8.6 5.4D21P (T-e) 26.7 8.0 8.093357 (T-e) 28.2 7.7 7.5D6 (T-e) 27.9 8.2 5.193360 (T-e) 30.0 9.5 4.5L10 (T-e) 28.0 7.9 5.5L12 (T-b) 24.5 5.0 2.9

Reptiles92154 (T-b) 23.6 7.1 3.893405 (T-b) 30.4 8.7 4.4D8 (T-b) 25.3 8.7 n.d.92210 (T-b) 27.4 8.0 4.293369 (T-b) 27.3 6.5 7.0L11 (T-b) 26.0 8.5 4.4

aNd, not determined.


Additionally, no evidence for excessive evaporation overprecipitation is provided by the sedimentary record in thewestern domain of the Anglo-Paris basin. The highest d18Ofish values are observed in the Boulonnais (Samples D35,D71, P12; Table 1; Figures 1 and 4) where estimatedwater depths are 50–200 m for the upper to lower offshoredeposits [Vidier et al., 1995; Garcia et al., 1996].[30] An apparent variation in the isotopic temperatures of

15�C is observed over a 3� change of paleolatitudes betweenthe Boulonnais and the Burgundy platform (Figures 4 and 7).Such a thermal gradient of 5�C/�Lat. is unrealistically toohigh when compared to modern thermal gradients that aregenerally lower than 1�C/�Lat [Savin, 1977] (see also http://ingrid.ldeo.columbia.edu)[31] For the middle-late Bathonian, we observe that the

d18O fish values progressively decrease along a north-southdirection (Figure 7). This distribution may be due to theinflux of a cool current that progressively becomes warmersouthward. This water mass of boreal origin probably had ad18O value lower than that more typical of tropical waters,taken here to be 0%, consequently, calculated temperaturesmust be considered as maximal values. During the lateBathonian, isotopic temperatures may have been close to(1) 19�C in the northern part of the basin, in the Boulonnaisand Normandy, (2) 24�C in the central part and, (3) 28–31�C in the southeast. Such temperature gradients of 10�Cover a few hundred kilometers have modern analogues suchas the area between the east U.S. coast and Bermuda wherethe Gulf Stream heads northeast from the Sargasso Sea[Brown et al., 1989]. The proposed cool current may have

resulted from the opening of the North Sea rift that wasinitiated during the middle-late Bathonian [Ziegler, 1988].Cool waters, formed at high paleolatitudes in the BorealArctic domain, could have flowed southward to mix pro-gressively with the western Tethys. The connection betweenthe basins was probably limited during the middle Batho-nian; during this period, corridors were filled with protectedsandy environments and deltaic shales, both characterizingwater depths less than 30 m [Ziegler, 1988]. The late-Bathonian Eudesia isochron corresponds to the most exten-sive flooded surface and coincides with the first briefexcursion of boreal ammonites into the Anglo-Paris Basin[Marchand and Thierry, 1974, 1997; Cariou et al., 1985],confirming a real communication between the Tethyan andBoreal basins and the influx of cold waters.

6.4. Middle-Late Jurassic Evolution of Tropical SSTin the Anglo-Paris Basin

[32] At tropical latitudes, the evaporation/precipitationratio tends to be higher than 1 resulting in increased salinityand d18O values of surface waters relative to mean oceanwater. 18O-enrichment of about 1% relative to SMOW hasbeen documented for present-day tropical surface waters[e.g., Craig and Gordon, 1965; Carpenter and Lohmann,1995; Gonzalez and Lohmann, 1985]. Therefore isotopictemperatures of surface waters have been derived from thed18O record of biogenic phosphates through the Middle-Late Jurassic (�20 Myr), assuming a d18O seawater of 0%.This hypothesis has been retained considering both thetropical paleolatitudes of western Europe and the absence

Figure 6. Oxygen isotope fractionation between present-day shark phosphate and ambient seawater.Data come from Picard et al. [1998]. Note that this equation is comparable to the equation published byKolodny et al. [1983], which was determined by using modern fresh and sea water fish species.


of polar ice caps as a first approximation. Sea surfacetemperatures (SST) inferred from surface dwellers (Aster-acanthus and Pycnodontidae) increased from 25�C to 30�Con average over �7 Myr from late Bajocian to late Batho-nian then decreased down to 20�C in the middle Oxfordianboundary in �8 Myr (Figure 8). This thermal minimum isfollowed by a warming of 5�C of surface waters during thelate Oxfordian and early Kimmeridgian.[33] The apparent cooling of surface waters that was

initiated during the late Callovian Lamberti zone and thatattained a maximum during the early-middle Oxfordianrelates with the colonization of the western Tethys by theboreal ammonites of the Cardioceratidae family [Marchandand Thierry, 1974, 1997; Cariou et al., 1985]. Such acooling episode may have corresponded to the southwardpropagation of a boreal oceanic current and/or to a global

climate change. There is no available evidence for theexistence of a cold oceanic current throughout the majorpart of the Oxfordian. Studies of the distribution of thewood genus Xenoxylon and palynomorphs argue for atemperate and wet climate during the early Oxfordian inwestern Europe [Philippe and Thevenard, 1996; Abbink etal., 2001]. All these data support the existence of a coolingepisode that affected both marine and terrestrial environ-ments of the western Tethyan domain.[34] Perturbations of the carbon cycle due to volcanism or

changes in the rates of burying organic matter could haveinduced temperature oscillations at the timescale of a fewmillion years. According to Dromart et al. [1996], the warmBathonian-Callovian phase could be related to large CO2

fluxes released by contemporaneous arc-related volcanismin Patagonia at 164.1 Myr [Feraud et al., 1999] and South

Figure 7. Geographical map of the Anglo-Paris Basin with the regional distribution of fish tooth d18Ovalues for the middle-late Bathonian. The gray area encloses isotopic compositions higher than 20%.This regional distribution of d18O values could have resulted from the presence of a cold oceanic currentoriginating from boreal realms.


China at 164.6 Myr [Davis et al., 1997]. Organic rich-layersdeposited during the middle Callovian could have seques-tered carbon and lowered atmospheric CO2 levels, thusinitiating the global cooling stage at the Callovian-Oxfordianboundary.[35] With the hypothesis of a constant isotopic composi-

tion of seawater of 0%, we calculated tropical surfacetemperatures ranging from 25�C to 30�C for the easternbasin during the Bajocian throughout the Callovian. Thistemperature range is slightly higher than modern thermalvariations (19�C to 27�C) measured in shallow waters(�50 m) under similar latitudes (20–30�) in analogouscarbonate platforms [Adlis et al., 1988] (Ocean Atlas data,Scripps Institute of Oceanography). By contrast, middleOxfordian isotopic temperatures of 20�C are rather lowconsidering the presence of coral reefs in the Swiss Jura[e.g., Gygi and Persoz, 1986]. The apparent low sea surfacetemperatures during the Oxfordian could result from anerroneous estimate of the oxygen isotope composition ofambient seawater. A cooling stage could have been accom-panied by the growth of a polar continental ice cap. Theformation of a polar ice cap, even limited in size, could haveled to a positive shift in the d18O of seawater in theOxfordian relative to the Callovian. This change would berecorded in the d18O values of fish tooth enamel. Thepossible ice volume component of the d18O fish recordcannot be simply determined without a knowledgeconcerning the extent of glacial sediments, the relative sea-level change, and the d18O value of Jurassic continental ice.However, basic calculations can provide first-order esti-mates. During Quaternary peak glacial times, most of the

tropical surface temperatures cooled no more than 2–3�Cwith local exceptions around 5�C [e.g., Broecker, 1992].Relative to the observed isotopic shift of 1.5% observedduring early-middle Oxfordian, a d18O variation of 0.5%could be attributed to the ice volume component, assumingsimilar thermal variations for Jurassic and modern tropicalsurface waters. Considering an oxygen isotope compositionfor continental ice in the range �40 to �30%, the mass ofcontinental ice would range between 2 � 1019 kg and 3 �1019 kg, and a fall in sea-level of about 50 m. Dromart et al.[2003] recently suggested the formation of polar ice toaccount for large-scale sea-level change, documented world-wide and of eustatic origin, with a maximum in the lateCallovian. The geological evidence are (1) the occurrence ofglendonites in the sediments of northern Asia, (2) depositionof deep-sea fans in Oman, (3) seaward migration of shore-lines (North Sea), (4) valley incision in south Portugal andSaudi Arabia, and (5) subaerial exposures of marine sedi-ments in Portugal, Israel, Alaska and Argentina. As noted byDromart et al. [2003], the abrupt and global marine regres-sion of the late Callovian follows the decrease of sea surfacetemperatures along with a southward migration of borealammonites. Therefore a glacial event is presented as aplausible scenario that could conciliate isotopic, paleonto-logical and geological data.[36] Similarly to biocarbonate systems, interpretation of

the bioapatite d18O value in terms of temperature dependscritically on the choice of the d18O seawater value. Ourproposed temperatures may have to be revised, by probablyless than three or four degrees, if independent evidence isfound for a value other than 0% for d18O seawater. The

Figure 8. Evolution of isotopic temperatures calculated with a d18O of seawater = 0%, from theBajocian to the Tithonian. The area between the two horizontal plain lines covers the present-day range ofsea surface tropical temperatures. The fitting curve was obtained by using only the Asteracanthus andPycnodont assemblages (filled circles) from the eastern part of the basin using a least square method with20% weight. Open circles indicate tearing sharks.


presence or absence of continental polar ice caps is a crucialelement in this discussion. From a purely isotopic point ofview for the period from the Bajocian through to theThithonian (Figure 8), a tentative case can only be madefor the presence of a significant continental ice reservoirduring the Oxfordian, the Thithonian and perhaps the Bajo-cian-Bathonian, the three stages with relatively high d18Oapatite values. These propositions are supported, in part, bythe documented periods of major regression [Guillocheau,1991; Garcia et al., 1996] and occurrence of possible glacialphenomena in other part of the world [Price, 2000].

7. Conclusion

[37] Oxygen isotope compositions of marine vertebratetooth enamel, that were not diagenetically altered, vary from18.5 to 22.5% for the Middle-Late Jurassic of the westernTethyan basin. These data are interpreted as evidence forthermal variations of sea surface (�100 m) temperaturesover a few Myr scale. A drop of isotopic temperatures(about 3�C to 5�C) occurred around the Callovian-Oxfor-dian boundary. This cooling of surface waters is associatedwith the southward migration of boreal ammonites and thedevelopment of temperate flora in the Anglo-Paris Basin.This cooler episode precedes a thermal increase that beganduring the late Oxfordian until the Kimmeridgian. Apparentisotopic temperatures not exceeding 20�C are low fortropical latitudes even when assuming an isotopic compo-sition of seawater of 0% compatible with 18O-enriched low-

latitude sea surface waters and the absence of permanentwell-developed polar ice caps. Therefore we cannot excludethe existence of an Oxfordian glaciation event that couldexplain the contemporaneous southward migration of borealammonites and the global sea-level fall.[38] Strong oxygen isotope gradients (3%) over 500 km

from the northwest to the southeast of the basin suggest thedevelopment of a cool oceanic current during the middle-late Bathonian that could be related to the opening of theNorth Sea rift. According to paleontological and paleobo-tanical studies, we suggest that the late Callovian-earlyOxfordian thermal decrease could be the expression of aglobal event rather than a more local geographic effect ofthese cool oceanic currents. In the absence of isotopicrecords provided by foraminifera, those available from fishphosphatic remains reveal that Jurassic climates were not soconsistently warm and equable as previously thought.

[39] Acknowledgments. Sampling would not have been possiblewithout the help of A. Prieur (Universite Claude Bernard de Lyon),B. Laurin, J.-H. Delance (Universite de Bourgogne), M. Weidmann(Universite de Lausanne), A. Boullier (Universite de Besancon), A. Lena,G. Gallio (Museum de la Citadelle, Besancon), J. P. Goujon (MNHN,Paris), Museum de Bale, J. M. Mazin (Universite de Poitiers), and G. Breton(Museum du Havre), who provided some of the vertebrate samples. We alsothank M. Emery for her help in sample analyses. The authors thank thereviewers David Dettman and Christina Hartman, who helped us toimprove the scientific content of this manuscript. This work was supportedby the CNRS through the programs ‘‘Interieur de la Terre’’ (Comportementdynamique des plates-formes carbonatees) and ‘‘ECLIPSE.’’

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��G. Dromart, P. Grandjean, C. Lecuyer, and

S. Picard, Laboratoire Paleoenvironnements etPaleobiosphere, CNRS UMR 5125, Campus de laDoua, Universite Claude Bernard Lyon 1, F-69622 Villeurbanne, France.([email protected]; [email protected];[email protected]; [email protected])J.-P. Garcia, Centre des Sciences de la Terre,

CNRS UMR 5561, Universite de Bourgogne,6 Boulevard Gabriel, F-21000 Dijon, France.([email protected])S. M. F. Sheppard, Laboratoire de Sciences de

la Terre, CNRS UMR 5570, Ecole NormaleSuperieure de Lyon, 46 allee d’Italie, F-69364Lyon, France. ([email protected])


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Thermal evolution of Tethyan surface waters during the Middle-Late Jurassic: Evidence from δ 18 O values of marine fish teeth